It has been the practice when sampling molten unkilled steel to use in the sampling device a killing agent such as aluminum, zirconium, silicon or titanium. The unkilled steel is introduced into a cavity in the sampling device where the killing agent is present in sufficient quantity to combine with the available oxygen of the molten sample so that upon freezing of the sample there will be no substantial loss of oxygen content and no porosity which will interfere with analysis. When used in this sense, the terms "killed" and "killing" do not have the same meaning that they would have in refining operations where such terms indicate deoxidation of the molten steel to such an extent that it will lie quiescent when poured into an ingot mold. Obviously, such a deoxidation procedure would not be used if one intended to analyze the oxygen content of a sample of the molten steel since it would be self-defeating. Therefore, when used in the present disclosure, the terms "killed" or "killing" should be construed as the chemical combination of a metal with available, i.e., free, oxygen in a sample.
The use of previously known killing agents in sampling has many attendant problems. For example, when aluminum or silicon are used, two samples must be taken since the analysis of steel usually seeks silicon and aluminum content. The same is often true in the case of zirconium and titanium. Zirconium has the additional disadvantage of making the solidified sample hard and therefore more difficult to work with. Titanium also has an additional disadvantage in that it makes the sample tough and more difficult to work with. Perhaps most disadvantageous, titanium is difficult to melt in sampling devices and unmelted concentrations of titanium throw the analysis results off. Even when it does melt, titanium, and other previously known killing agents, will react with at least a portion of the available nitrogen in the sample to form higher melting nitrides and thus promote inaccurate nitrogen readings.
U.S. Pat. No. 3,704,621 proposes the use of magnesium in lieu of the above killing agents in sampling molten unkilled steel and it does an excellent job. However, its use is limited, and special care is required to avoid the propinquity of the magnesium to combine with air at molten steel temperatures and create explosive conditions.
As a result of all the foregoing, the steel industry has lacked a satisfactory killing agent for use in the sampling of molten steel.